<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 300px;
            height: 300px;
            border: 2px solid saddlebrown;
        }
        
        .box1 {
            border-radius: 15px;
        }
        
        .box2 {
            border-radius: 15px 30px;
        }
        
        .box3 {
            border-radius: 5px 30px 30px 60px;
        }
        
        .box4 {
            border-radius: 300px 0 0 0;
        }
    </style>
</head>

<body>
    <div class="box1">每个角都是15px</div>
    <div class="box2">左上和右下15px，右上和左下是30px</div>
    <div class="box3">左上5px，右上和左下是30px，右下是60px</div>
    <div class="box4">半圆</div>
</body>

</html>